Multi-fuel combustion system

ABSTRACT

The present invention explains a multi-fuel combustion system. It consist of a combustor basket adapted to combust at least two type of fuels. The combustor basket has got a circumferential wall comprising a plurality of openings. The combustion system further has a first conduit adapted to provide a first type of fuel directly to the combustor basket, a second conduit adapted to provide a second type of fuel directly to the combustor basket and a third conduit adapted to inject at least one of the first type of fuel and the second type of fuel through the openings into the combustor basket.

FIELD OF INVENTION

The present invention lies in the field of combustion turbines inparticular for generating electrical energy and more particularly, tocombustor baskets employed therein.

BACKGROUND OF INVENTION

Future energy demand, scarcity of available fuels and environmentalregulations put pressure on power plant producers to come up withsolutions for safe, efficient and clean ways to generate power. Thescarcity of fuels mainly applies to oil and to a lesser extend tonatural gas. With an availability of coal in abundance, electricityproduction from coal is mostly done using steam power plants. A cleanerand more efficient option to generate power from coals is to use them inan integrated gasification combine cycle (IGCC). In an IGCC, coals arefirst gasified to yield syngas, consisting mainly of CO (carbonmonoxide) and H₂ (hydrogen).

Syngas typically has a significantly lower calorific value as comparedto conventional natural gas fuels. By removing the CO content from thesyngas prior to combusting it, one also has an effective means for CO₂(carbon-dioxide) capture. The IGCC concept with pre-combustion CO₂capture is one of the most cost-effective ways to produce electricityand avoid the emission of CO₂ in the future. The economical potential ofthe IGCC plant with CO₂ capture can increase even further when naturalgas prices rise faster than expected or with increased carbon taxregulation.

Due to the low calorific value and high hydrogen content, the combustionof syngas fuels requires the development of adapted or completely newcombustion systems which are able to handle the wide range of syngasfuels, and produce little emissions and can handle the high reactivityof the fuels.

The syngas fuel composition depends on the type of gasifier used and onwhether or not the CO is separated from the fuel. Besides syngas fuels,the combustion system might run on a second conventional fuel for backupand start up. The ideal possibility is to have all the different typesof fuels combusted in a stable way by one combustion system. To increasethe efficiency and compensate for the efficiency loss due to thegasifier and CO₂ separation techniques, the trend will be to increasepressure and turbine inlet temperatures, even beyond values wherecurrently natural gas experience is available. With these increasingpressures and temperatures, it becomes even more important to design acombustion system that is able to combust the syngas and hydrogen fuel,as danger for burner overheating and thermo acoustic excitationtypically increases with pressure and temperature.

SUMMARY OF INVENTION

In view of the foregoing, an embodiment herein includes a multi-fuelcombustion system comprising: a combustor basket adapted to combust atleast two type of fuels, said combustor basket having a circumferentialwall comprising a plurality of openings; a first conduit adapted toprovide a first type of fuel directly to the combustor basket; a secondconduit adapted to provide a second type of fuel directly to thecombustor basket; and a third conduit adapted to inject at least one ofthe first type of fuel and the second type of fuel trough the openingsinto the combustor basket.

In view of the foregoing, another embodiment herein includes a method ofoperating a multi-fuel combustion system comprising a first phase and asecond phase, wherein the first phase comprises: providing ignition to acombustor basket to ignite a first type of fuel, where the first type offuel is supplied to the combustor basket through a first conduit;supplying steam to the first conduit in addition to the first type offuel and supplying steam to the second conduit after the ignition; andwherein the second phase comprises: supplying a second type of fuel tothe combustor basket after ignition of the first fuel through the secondconduit, while stopping the supply of the first fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described hereinafter with reference toillustrated embodiments shown in the accompanying drawings, in which:

FIG. 1 illustrates a longitudinal cross-section of the multi-fuelcombustion system,

FIG. 2 shows fuel injector holes at the region of nozzle of the firstand the second conduits,

FIG. 3 shows the fuel injector holes of the first conduit based on apreferred embodiment of the invention,

FIG. 4 illustrates a first embodiment of cross section of the combustorbasket taken along the plane 2-2 a of FIG. 1,

FIG. 5 illustrates a second embodiment of cross section of the combustorbasket taken along the plane 2-2 a of FIG. 1,

FIG. 6 illustrates a third embodiment of cross section of the combustorbasket taken along the plane 2-2 a of FIG. 1,

FIG. 7 illustrates the arrangement of the wall of the combustor basket,

FIG. 8 illustrates the rib structure of the cylindrical region of thecombustor basket, and

FIG. 9 illustrates a transition and a flow conditioner arrangementaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

In general terms, a combustion turbine comprises three sections: acompressor section, a combustor section having a typical combustorbasket and a turbine section. Air drawn into the compressor section iscompressed. The compressed air from the compressor section flows throughthe combustor section where the temperature of the air mass is furtherincreased after combustion of a fuel. From the combustor section the hotpressurized gas flow into the turbine section where the energy of theexpanding gases is transformed into rotational motion of a turbine rotorthat drives an electric generator.

The lower calorific value of the syngas fuels and the necessity to alsooperate the burner on a backup fuel like natural gas, significantlyaffects the design of the burners. The burner should be able to handlelarge fuel mass flows and the fuel passages consequently need to have alarge capacity. A too small capacity results in a high fuel pressuredrop. Due to the large fuel mass flow involved, a high pressure drop hasa much larger impact on the total efficiency of the engine as comparedto a typical natural gas fired engine.

FIG. 1 illustrates a cross-sectional view of the multi-fuel combustionsystem 10 according to one embodiment of the invention. A multi-fuelcombustion system 10 comprises a combustor basket 12. The wall 16 of thecombustor basket 12 is made of multiple cylindrical regions 14 arrangedto overlap each other at the transition and extends from an upstream end20 to a downstream end 22 of the combustor basket. The upstream end 20of the combustor basket is close to the region, where the fuel conduitsgenerally supply the fuels for the combustion and the down stream end isthe region, where the gas after combustion flows out to of the combustorbasket to a turbine section. The combustion system 10 is designed tocombust at least two type of fuels, for example natural gas and syngas.The types of fuels that could be used are not restricted to natural gasand syngas and hence the combustion system 10 could use other fuels forcombustion.

FIG. 1 further shows a first conduit 24 adapted to provide a first typeof fuel, for example natural gas, directly to the combustor basket 12and the second conduit 26 is adapted to provide a second type of fuel,for example syngas directly to the combustor basket 12. Also there is atlast one third conduit 25 adapted to inject at least one of the firsttype of fuel and the second type of fuel through one or multipleopenings 18 into the combustor basket 12. There could be more than oneconduit to provide each type of fuel to the combustor basket based onthe design and requirement. For example, there could be multiple thirdconduits 25 to supply the fuel through multiple openings 18 in thecombustor basket 12. Also based on the mode of operation of thecombustor basket 12, each of the conduits is adapted to handle adifferent fuel. Even the conduits could handle multiple fuels at thesame point of time. The second conduit 26 is positioned to encircle thefirst conduit 24 or concentrically arranged for effective delivery ofthe fuels. The first conduit 24 is positioned coaxially, and internally,of a larger diameter second conduit 26. Since the diameter of the secondconduit 26 is greater that the first conduit 24, the said second conduit26 can handle low calorific value fuels of larger volumes since largefuel mass flows is needed to achieve a certain thermal power input.

The third conduit 25 is adapted to inject at least one of the first typeof fuel and the second type of fuel into a compressor discharge air thatflow through at least one of the openings 18 associated with at leastone of the cylindrical regions 14. The third conduit 25 has a fuelinjector nozzle 27 at the end having 1 to 5 injector holes that areaimed at an angle of 0 to 90° relative to a centerline of the opening18. The first conduits 24 and the second conduit 26 under considerationconsist of concentric circles of circular holes at the region of nozzle28 of the conduits which acts as injectors for the fuels. The nozzle 28helps to inject the respective fuels directly into the combustor basket12 and is positioned at the upstream end 20 of the combustor basket 12.

FIG. 2 shows explicitly these two rows of concentric holes at the regionof nozzle 28. Each circle of rows is associated to a conduit. The innerrow of holes 21 corresponds to the first conduit 24 and the outer row ofholes 23 corresponds to the second conduit 26. The number of injectorsin each conduit can vary, for example between 8 to 18 holes, but is notrestricted to this numbers. A preferred embodiment having 14 injectorsfor both conduits is shown in FIG. 2. The holes can be clocked relativeto each other or can be inline.

In another preferred embodiment, the holes in the region of nozzle 28 ofthe first conduit 24 comprises multiple holes positioned at, at leasttwo different radial distances from the center of the nozzle forinjecting a fuel flow into a region of combustion in the combustorbasket 12. This nozzle design promotes a greater amount of fuel flowtowards the center of the nozzle, which cools the nozzle in a costeffective and simple manner. Most importantly the hole arrangementmaintains the aerodynamic performance of the nozzle. FIG. 3 shows such anozzle 30, of such a type used by the first conduit 24 to inject thefuel to the combustor basket 12. The first set of holes 32 and thesecond set of holes 34 are arranged at a first radial distance 31 and ata second radial distance 33 respectively from the center 36 of thenozzle.

Coming back to FIG. 1, the circumferential wall 16 of the combustorbasket 12 comprises multiple openings 18. At least two of thecylindrical regions 14 a and 14 b nearer to the upstream end 20 of thecombustor basket 12 further comprise multiple openings 18 distributedalong the circumference of the respective cylindrical regions. Thismultiple openings 18 allow a compressor discharge air from a compressorstage to flow towards a region of combustion in the combustor basket. Atthe same time, at least one of the cylindrical region near to thedownstream end 22 of the combustor basket 10 may also comprise pluralityof openings 18 distributed along the circumference of the cylindricalregion to allow the compressor discharge air to flow towards a region ofcombustion in the combustor basket 12.

FIG. 4 illustrates a first embodiment 40 of cross section of thecombustor basket 12 taken along the plane 2-2 a of FIG. 1. The number ofopenings in the individual cylindrical region 14 varies between 5 and 9based on the embodiments. FIG. 4 shows 6 numbers of openings 18 in thecircular region 14 of the combustor basket 12.

FIG. 5 illustrates a second embodiment 50 of cross section of thecombustor basket taken along the plane 2-2 a of FIG. 1. FIG. 5 shows 7numbers of openings 18 in the circular region 14 of the combustor basket12.

FIG. 6 illustrates a third embodiment 60 of cross section of thecombustor basket 12 taken along the plane 2-2 a of FIG. 1. FIG. 6 shows9 numbers of openings 18 in the circular region 14 of the combustorbasket 12. These openings in the combustor basket are like scoops,especially radial scoops through which compressor discharge air isinjected in the combustor basket 12. The openings are alternativelyreferred to as scoops in few places in the description for convenience.

At a minimum, the length of the scoops is half the diameter of thescoop. For example, FIG. 6 shows an opening 18, having a length 43 and adiameter 41. This length is oriented to the interior region of thecombustor basket 12. This length helps to lead the air further into thecombustion region. The scoops deliver air flow with greater penetrationinto the fuel stream, achieving improved heating efficiency and morecomplete combustion. The openings 18 are equally distributed along thecircumference of the cylindrical region 14. Odd numbers of openings arebeneficial for wall temperatures and helps against thermo-acousticproblems, since they provide a rotational asymmetrical configuration.The scoops can be circular or oval in cross-section. When the scoops areoval, the smallest dimension of the oval shape lies in the direction ofthe basket centerline. The scoops can have an angle of 0-45° relative tothe radial direction, from the basket centerline and aiming downstreamwhen angled. In a particular layout, few or all the scoops in acylindrical region can have an angle of 15°, whereas few or all thescoops in another cylindrical region can have an angle of 0°, i.e. aimedradial towards the center line. In addition, the scoops can be directedagainst the flow of thrust of the combustor system with an angle up to15° relative to radial direction. In another alternate embodiment, thedownstream edges of the scoops are cut-off at an angle between 0-60°relative to the centerline of the combustor basket. This is basically toavoid damages caused by the recirculation of hot air to the scoops.

The combustion system 10 further comprises a cover plate 29 coupled tothe combustor basket 12 and the first, second and third conduits. Thisenables the combustor basket and the conduits to be attached to acasing.

FIG. 7 illustrates the arrangement 70 of the wall 16 of the combustorbasket. As mentioned, the wall 16 of the combustor basket 12 is made ofa plurality of cylindrical regions 14 arranged to overlap each other atthe transition. The individual cylindrical region 14 comprises an outersurface 72, said outer surface 72 is provided with a rib structure 82 asshown in FIG. 8. The outer surface 72 is covered substantially by aperforated layer 74 adapted to provide an air flow for cooling the wall16. The wall 16 of the combustor basket 12 is cooled by convection andeffusion cooling. To increase the effectiveness of the cooling method,so-called plate fin design as shown in FIG. 7 is used. These plate finsconsist of two liners. The inner liner, which is basically thecylindrical region is provided with the cooling rib structure 82 in theouter surface 72 to increase the cooling surface. The outer liner is theperforated layer 74. When the cooling air exits the plate fin, it servesas effusion cooling air.

The multi-fuel combustion system 10 further comprises a flow conditioner45 positioned to encircle the combustor basket 12 and having a conicalsection 46 and a cylindrical section 47 having plurality of holes 48adapted to allow the compressor discharge air to flow towards a regionof combustion in the combustor basket 12. The flow conditioner 45 isused to achieve the pressure drop required for cooling and to provide auniform air flow towards the region of combustion in the combustorbasket 12. Holes 48 in both the cylindrical section 47 and the conicalsection 46 are used as flow passage for air.

In addition, as shown in FIG. 9, a gap 92 exists between the transition94 and the end 96 of the conical section 46 of the flow conditioner 45.The flow conditioner 45 slightly overlaps the transition 94. In this waythermal expansion does not affect the flow area of the gap 92. Theconical section 46 and a cylindrical section 47 is connected together bya flange or could be welded together.

The multi-fuel combustion system 1 of FIG. 1 further comprises an exitcone 35 at the downstream end 22 of the combustor basket 12 havingmultiple slots 37 aligned to the plurality of openings 18 associatedwith at least one of the cylindrical regions 14. This exit cone 35 isintended to improve the mixing between the hot combustion gasses and thecold air flow coming out of a spring-clip passage 39. The improvedmixing between these flows lead to better CO emissions. The exit coneslots 37 aligned with the scoops 18 prevent overheating of the exit cone35.

The method of operating the multi-fuel combustion system 10 is nowdescribed. The operation could be divided into two main phases a firstphase and a second phase. During the first phase an ignition is providedto a combustor basket by an ignition coil to ignite a first type offuel, for example natural gas supplied to the combustor basket 12through the first conduit 24. The method also involves supplying steamto the first conduit 24 in addition to the first type of fuel andsupplying steam to the second conduit 26 after the ignition. Steam isprovided to the second conduit 26 at a time earlier than the steamprovided to the first conduit 24. The method further involves supplyinga medium, for example an inert gas, nitrogen, steam or seal air to thesecond conduit 26 during the first phase for stabilizing the combustionsystem 10 for any pressure difference in the combustor basket 12. In atypical industrial arrangement the combustion system or the turbinecomprises a plurality of combustor baskets, and while in operation therecould be pressure differences that could be built up between thesecombustor baskets. The supply of the medium also takes care of thispressure difference in the combustor basket due to this type ofarrangement. The supply of the medium in the second conduit 26 is shutoff once the steam supply is stabilized in the first conduit 24 and thesecond conduit 26 during the first stage of operation.

In the second phase of operation, a second type of fuel for examplesyngas is supplied to the combustor basket through the second conduit26, while stopping the supply of the first fuel. The method furthercomprises supplying a portion of the second type of fuel to thecombustor basket 12 through the first conduit 24 during the secondphase. The steam is continuously supplied in the first conduit 24 fromthe first phase until the beginning of supplying the portion of thesecond type of fuel through the first conduit 24 during the secondphase. Also the third conduit 25 may also be used to supply any one ofthe first or second type of fuel for enabling an effective and morecomplete combustion by introducing the said fuels through the openings18 if required. This further helps in reducing NOx emissions.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternate embodiments of the invention, will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that such modifications can be made withoutdeparting from the embodiments of the present invention as defined.

1. A multi-fuel combustion system comprising: a combustor basket adaptedto combust at least two type of fuels, said combustor basket having acircumferential wall comprising a plurality of openings to guide a flowof air into the combustor basket; a first conduit adapted to provide afirst type of fuel directly to the combustor basket; a second conduitadapted to provide a second type of fuel directly to the combustorbasket; and a third conduit adapted to inject at least one of the firsttype of fuel and the second type of fuel through at least one of theopenings into the combustor basket.
 2. The multi-fuel combustion systemaccording to claim 1, wherein the wall of the combustor basket is madeof a plurality of cylindrical regions arranged to overlap each other atthe transition and extends from the upstream end to the downstream endof the combustor basket.
 3. The multi-fuel combustion system accordingto claim 2, wherein the individual cylindrical region comprises an outersurface, said outer surface is provided with a rib structure and iscovered by a perforated layer adapted to provide an air flow for coolingthe walls.
 4. The multi-fuel combustion system according to claim 2,wherein at least two of the cylindrical regions at the upstream side ofthe combustor basket further comprise the plurality of openingsdistributed along the circumference of the cylindrical region to allow acompressor discharge air to flow towards a region of combustion in thecombustor basket.
 5. The multi-fuel combustion system according toclaims 2, wherein at least one of the cylindrical regions at thedownstream side of the combustor basket further comprises the pluralityof openings distributed along the circumference of the cylindricalregion to allow the compressor discharge air to flow towards a region ofcombustion in the combustor basket.
 6. The multi-fuel combustion systemaccording to claim 2, wherein the individual cylindrical regioncomprises between 5 and 9 openings.
 7. The multi-fuel combustion systemaccording to claim 6, wherein the individual cylindrical regioncomprises an odd number of openings.
 8. The multi-fuel combustion systemaccording to claim 1, wherein the first type of fuel is natural gas. 9.The multi-fuel combustion system according to claim 1, wherein thesecond type of fuel is syngas.
 10. The multi-fuel combustion systemaccording to claim 1, wherein the first conduit comprises a nozzle tosupply at least one of the first type of fuel and the second type offuel directly to the combustor basket for combustion, wherein the nozzlecomprises a plurality of holes positioned at, at least two differentradial distances from the center of the nozzle for enabling a fuel flowinto a region of combustion in the combustor basket.
 11. The multi-fuelcombustion system according to claim 1, further comprises an exit coneat the downstream end of the combustor basket comprising of plurality ofslots aligned to the plurality of openings associated with at least oneof the cylindrical regions.
 12. The multi-fuel combustion systemaccording to claim 1, further comprises a flow conditioner positioned toencircle the combustor basket and having a conical section and acylindrical section having plurality of holes adapted to allow thecompressor discharge air to flow towards a region of combustion in thecombustor basket.
 13. The multi-fuel combustion system according toclaim 1, further comprises a cover plate coupled to the combustor basketand the conduits, such that the combustor basket and the conduits areattached to a casing using said cover plate.
 14. The multi-fuelcombustion system according to claim 1, wherein the first conduit andthe second conduit is concentrically arranged for effective delivery ofthe first type of fuel and the second type of fuel to the combustorbasket.
 15. The multi-fuel combustion system according to claim 1,wherein the third conduit is adapted to inject at least one of the firsttype of fuel and the second type of fuel into a compressor discharge airthat flow through at least one of the openings associated with at leastone of the cylindrical regions.
 16. The multi-fuel combustion systemaccording to claim 1, wherein the third conduit further comprises aninjector nozzle having at least one hole to inject at least one of thefirst type of fuel and the second type of fuel into a compressordischarge air that flow through at least one of the openings associatedwith at least one of the cylindrical regions.
 17. A method of operatinga multi-fuel combustion system comprising a first phase and a secondphase, wherein the first phase comprises: providing ignition to acombustor basket to ignite a first type of fuel, where the first type offuel is supplied to the combustor basket through a first conduit;supplying steam to the first conduit in addition to the first type offuel and supplying steam to the second conduit after the ignition; andwherein the second phase comprises: supplying a second type of fuel tothe combustor basket after ignition of the first fuel through the secondconduit, while stopping the supply of the first fuel.
 18. A method ofoperating a multi-fuel combustion system according to claim 17, furthercomprising supplying a portion of the second type of fuel to thecombustor basket through the first conduit during the second phase. 19.A method of operating a multi-fuel combustion system according to claim17, wherein the first type of fuel is natural gas.
 20. A method ofoperating a multi-fuel combustion system according to claim 17, whereinthe second type of fuel is syngas.